Does neuromuscular activation capability explain mobility function among older men and women?

Authors: CLARK, DAVID - University Of Florida; REID, KIERAN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; PATTEN, CAROLYN - University Of Florida; PHILLIPS, EDWARD - Spaulding Rehabilitation Hospital; RING, SARAH - Malcom Randall Va Medical Center; WU, SAMUEL - University Of Florida; FIELDING, ROGER - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Journal of the American Geriatrics Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2014
Publication Date: N/A
Citation: N/A

Interpretive Summary: Muscle activation is the signal from the nervous system to the muscles that is responsible for force production. Weakness in older adults is caused in part by reduced muscle activation. Age-related deficits in walking function are likely also caused by reduced muscle activation, but this remains unclear. The hypothesis of this study is that muscle activation of the quadriceps muscle group will be independently associated with walking speed in older men and women after accounting for other factors of potential importance, including muscle size, muscle fat content, body composition and age. Twenty six older men and eighteen older women (aged 70-85 years) participated in this study. Muscle activation was quantified using a technique called electromyography (EMG), which measures the electrical signals from the nervous system that trigger muscle contraction. We calculated the “rate of EMG rise”, which indicates how fast and how fully the muscles activate. In males, our analysis revealed that reduced rate of EMG rise was strongly predictive of slower walking speed. However, in females, our analysis revealed no significant relationship between rate of EMG rise and walking speed. These findings indicate that the capability to rapidly activate the quadriceps muscle group is an important factor accounting for walking speed among older men, but not among older women. This research is important for informing the design of assessments and interventions that seek to detect and prevent impairments that contribute to age-related mobility disability.

Technical Abstract: Age-related impairment of neuromuscular activation has been shown to contribute to weakness in older adults. However, it is unclear to what extent impaired neuromuscular activation independently accounts for decline of mobility function. The hypothesis of this study is that capability to produce rapid neuromuscular activation will be shown to be an independent determinant of mobility function in older men and women after accounting for muscle size and adiposity, body composition and age. The design will be Cross-sectional analysis. The setting will be at the University research center in Boston, Massachusetts. The participants are Twenty six older men and eighteen older women, aged 70-85 years. Mobility function assessed by 400-meter walk; neuromuscular activation of quadriceps assessed by surface electromyography (“rate of EMG rise”); thigh muscle cross sectional area and adiposity assessed by computed tomography; body composition assessed by body mass index. The multiple regression model for males accounted for 72% of the variability in walking speed (p<.0001), with age and rate of EMG rise as the dominant variables in the model. The multiple regression model for females accounted for 44% of the variability in walking speed, though the total model was not statistically significant (p=.18). However, the variables of age and subcutaneous adipose approached significance. The present findings indicate that the capability to rapidly activate the quadriceps muscle group is an important factor accounting for inter-individual variability of walking speed among older men, but not among older women. This research is important for informing the design of assessments and interventions to detect and prevent impairments that contribute to age-related mobility disability.